Biomedical subjects

Robert Poulin

Publications and source records attributed to Robert Poulin.

41 records · Page 3Linked to original sources

PubMed2002

The predictability of helminth community structure in space: a comparison of fish populations from adjacent lakes.

Patterns in helminth community structure can suggest that various processes are acting to shape parasite communities into organised, non-random assemblages of species. It is not clear, however, whether a pattern observed in one host population at one time would be observed again at another time, or at the same time in a different but comparable host population. Here, we test the repeatability of parasite community structure in space, and to a lesser extent time, with data on helminth parasites of two fish species, perch Perca fluviatilis and roach Rutilus rutilus, collected in different seasons from four adjacent lakes in Central Finland. Since populations of the same fish species harbour the same parasite species and were sampled in the same way, we would expect similar patterns in the structure of their helminth parasites if the same structuring processes are acting in all lakes. We found that no pairwise association between the most common helminth species were observed consistently between seasons within lakes, or among lakes during the same season. Similarly, nested subset patterns of species assembly were observed in some samples, but not consistently between seasons or among lakes. The lack of repeatability in space and between seasons shown by these analyses indicates that although helminth community structure often departs from randomness, it does not do so in a consistent and predictable manner. There may be some general, large-scale processes acting to structure helminth communities, but local or seasonal influences can often either mask their action, or play more important roles themselves.

Animals↗

PubMed2002

Trematode life cycles: short is sweet?

Complex life cycles are a hallmark of parasitic trematodes. In several trematode taxa, however, the life cycle is truncated: fewer hosts are used than in a typical three-host cycle, with fewer transmission events. Eliminating one host from the life cycle can be achieved in at least three different ways. Some trematodes show even more extreme forms of life cycle abbreviations, using only a mollusc to complete their cycle, with or without sexual reproduction. The occurrence of these phenomena among trematode families are reviewed here and show that life cycle truncation has evolved independently many times in the phylogeny of trematodes. The hypotheses proposed to account for life-cycle truncation, in addition to the factors preventing the adoption of shorter cycles by all trematodes are also discussed. The study of shorter life cycles offers an opportunity to understand the forces shaping the evolution of life cycles in general.

Adaptation, Physiological↗

PubMed2002

Thaumamermis zealandica n sp (Mermithidae: Nematoda) parasitising the intertidal marine amphipod Talorchestia quoyana (Talitridae: Amphipoda) in New Zealand, with a summary of mermithids infecting amphipods.

A new nematode, Thaumamermis zealandica n. sp. (Mermithidae; Nematoda), is described parasitising the intertidal marine amphipod Talorchestia quoyana Milne-Edwards (Talitridae) from the coast of South Island, New Zealand. The new species is characterised by the degree of dimorphism of the spicules, the arrangement of the genital papillae, the shape and length of the vagina and the anteriorly-placed amphids. This is the first known marine host of a member of the family Mermithidae. Published records of mermithid nematodes from amphipods are presented.

Amphipoda↗

PubMed2002

Qualitative and quantitative aspects of recent research on helminth parasites.

Relationships between the species diversity of different taxa, the mean number of articles published per year on each taxon, and the mean impact factor of the journals in which they appear, were examined across six taxa of helminths: Nematomorpha, Acanthocephala, Monogenea, Trematoda, Cestoda and Nematoda, the latter including only animal parasitic nematodes. The mean annual output of scientific articles per taxon was not related to the species diversity of these taxa or, at least, not significantly. Thus, the large volume of publications on nematodes is not merely a reflection of their estimated diversity. There were significant differences among taxa in the mean impact factor of the journals in which papers on each taxon appeared, with nematodes having the highest mean score, followed by trematodes and cestodes. In addition, across the six taxa, the mean journal impact factor correlated positively and significantly with the mean annual number of papers published: not only are there more papers published on nematodes and trematodes than on nematomorphs or acanthocephalans, but they are also generally published in higher-ranking journals. These results suggest that there is an increasing gap in the quantity and general importance of the research carried out on different helminth taxa.

Animals↗

PubMed2002

Can helminth community patterns be amplified when transferred by predation from intermediate to definitive hosts?

Helminth communities in definitive hosts are formed by the acquisition of packets of larvae arriving each time an intermediate host is consumed. It is thus possible that associations between parasite species or other aspects of community structure get transferred from intermediate to definitive hosts. Earlier computer simulations showed that associations between 2 parasite species, in particular positive associations, could be transferred up the food chain. Here, we alter some of the assumptions of previous models and generate new simulations of several ways in which source infracommunities in intermediate hosts can be transferred to target infracommunities in definitive hosts. In particular, we introduced nonrandom selection of intermediate hosts by predatory definitive hosts, to mimic the phenomenon of host manipulation by parasites; this consisted in biasing predation toward intermediate hosts harboring a certain parasite species. Overall, our results show that positive covariances between 2 parasite species can not only be transferred but can also be amplified during transmission to definitive hosts; significant covariance between parasite species can even appear in the definitive hosts when none existed in the intermediate hosts. Negative covariance was not as readily transferred to definitive hosts and amplified, in part because of properties of the presence-absence covariance index. Amplification of covariance results from intermediate host manipulation as well as from other processes taking place during transmission. These results suggest that the patterns of association between helminth species in definitive hosts cannot be taken to reflect the processes acting inside those hosts: they may simply be inherited, with amplification, from intermediate hosts.

Animals↗